Question: $\text E = \left[\begin{array}{rr}1 & 4 \\ 4 & -1\end{array}\right]$ What is the determinant of $\text E$ ?
Answer: The determinant of a 2x2 matrix can be computed the following way: $ \left|\begin{array}{rr}a & b \\ c & d\end{array}\right| = (a \times d)-(b \times c) $ In this specific case, $ \left|\begin{array}{rr}1 & 4 \\ 4 & -1\end{array}\right| = (1 \cdot -1)-(4 \cdot 4) $ $ = -17 $